Docker's v2 image format was the starting point for OCI, which is a later standard (and: actually a standard with multiple implementations, rather than a single implementation).

This is much more noticeable when you run into Docker v1 and Docker v2 images. They're quite different under the hood. In particular it means that OCI images can perform "layer rebasing" and "cross-repository blob mounting". Updating a layer of an image goes from O(n) to O(1).